Counter i guess then

Sale 1:

https://marketplace.tf/items/30316;5;u107

http://prntscr.com/faaaw0

Sold for $50 / 2.1 = ~24 Keys

Sale 2:

http://backpack.tf/profiles/76561198082929950#!/compare/1480636800/1494720000

http://backpack.tf/profiles/76561198220101208#!/compare/1491091200/1491177600

???

Sale 3:

http://backpack.tf/profiles/76561198170276601#!/compare/1491955200/1492128000

http://backpack.tf/profiles/76561198079098551#!/compare/1492041600/1492128000

Looks like it sold for the stash, way too high

Sale 4:

http://backpack.tf/profiles/76561198079098551#!/compare/1492387200/1492473600

Bulk, would end up at 16

Sale 5:

http://backpack.tf/profiles/76561198179779561#!/compare/1494720000/1494806400

Sold with ~2 keys in sweets for Circling TF Logo Defiant Spartan (20) = 18 Keys

Sale 6:

http://backpack.tf/profiles/76561198191023886#!/compare/1495152000/1495238400

Sold with THE SAME 2 keys in sweets for Terror-Watt Bubble Pipe (19) = 17 Keys

Mini for Bubble Pipe

http://backpack.tf/profiles/76561198105321885#!/compare/1494979200/1495065600

Sold for Infernal Flames Taunt: Spent Well Spirits (~19) = 19 keys

Sale 7:

http://backpack.tf/profiles/76561198262288177#!/compare/1495238400/1495324800

Sold with ~1 key in sweets for Green Confetti Thirst Blood (~19) + 4 Keys = 22 Keys

Sale 8:

http://backpack.tf/profiles/76561198186644131#!/compare/1491782400/1491868800

Sold for Duped Green Black Hole Berliner's Bucket Helm (31) = 31 Keys.

High, excluding

Mini for Bucket Helm

http://backpack.tf/profiles/76561198127735616#!/compare/1494892800/1495065600

Sold for 17 Keys + Kill-a-Watt Sober Stuntman (~14) = 31

Sale 9:

http://backpack.tf/profiles/76561198186644131#!/compare/1491868800/1492128000

Bulk

Sale 10:

http://backpack.tf/profiles/76561198000643699#!/compare/1491868800/1491955200

Sold for Miami Nights Towering Titanium Pillar of Hats (29) = 29 Keys

Mini for Tower:

http://backpack.tf/profiles/76561198161053005#!/compare/1494028800/1494115200

Sold for Blizzardy Storm Thirst Blood (29) = 29 Keys

High, countered by month seller @ 25, excluding

Sale 11:

http://backpack.tf/profiles/76561198129728237#!/compare/1491955200/1492041600

Sold with ~2 keys in sweets for Blizzardy Storm Hot Dogger (29) = 27 Keys

Countered by seller @ 25.

Sales at 17, 18, 22, 24

Taking 17-24 from Lemons' advice